Detailed Description

Note that since for the class we derive from, i.e. DoFAccessor<dim>, the two template parameters are equal, the base class is actually derived from CellAccessor, which makes the functions of this class available to the DoFCellAccessor class as well.

Conversion constructor. This constructor exists to make certain constructs simpler to write in dimension independent code. For example, it allows assigning a face iterator to a line iterator, an operation that is useful in 2d but doesn't make any sense in 3d. The constructor here exists for the purpose of making the code conform to C++ but it will unconditionally abort; in other words, assigning a face iterator to a line iterator is better put into an if-statement that checks that the dimension is two, and assign to a quad iterator in 3d (an operator that, without this constructor would be illegal if we happen to compile for 2d).

Copy operator. These operators are usually used in a context like iterator a,b; *a=*b;. Presumably, the intent here is to copy the object pointed to by b to the object pointed to by a. However, the result of dereferencing an iterator is not an object but an accessor; consequently, this operation is not useful for iterators on DoF handler objects. Consequently, this operator is declared as deleted and can not be used.

Return the result of the neighbor_child_on_subface function of the base class, but convert it so that one can also access the DoF data (the function in the base class only returns an iterator with access to the triangulation data).

Return the result of the periodic_neighbor_child_on_subface function of the base class, but convert it so that one can also access the DoF data (the function in the base class only returns an iterator with access to the triangulation data).

Return the values of the given vector restricted to the dofs of this cell in the standard ordering: dofs on vertex 0, dofs on vertex 1, etc, dofs on line 0, dofs on line 1, etc, dofs on quad 0, etc.

The vector has to have the right size before being passed to this function. This function is only callable for active cells.

The input vector may be either a Vector<float>, Vector<double>, or a BlockVector<double>, or a PETSc or Trilinos vector if deal.II is compiled to support these libraries. It is in the responsibility of the caller to assure that the types of the numbers stored in input and output vectors are compatible and with similar accuracy.

Return the values of the given vector restricted to the dofs of this cell in the standard ordering: dofs on vertex 0, dofs on vertex 1, etc, dofs on line 0, dofs on line 1, etc, dofs on quad 0, etc.

The vector has to have the right size before being passed to this function. This function is only callable for active cells.

The input vector may be either a Vector<float>, Vector<double>, or a BlockVector<double>, or a PETSc or Trilinos vector if deal.II is compiled to support these libraries. It is in the responsibility of the caller to assure that the types of the numbers stored in input and output vectors are compatible and with similar accuracy.

Return the values of the given vector restricted to the dofs of this cell in the standard ordering: dofs on vertex 0, dofs on vertex 1, etc, dofs on line 0, dofs on line 1, etc, dofs on quad 0, etc.

The vector has to have the right size before being passed to this function. This function is only callable for active cells.

The input vector may be either a Vector<float>, Vector<double>, or a BlockVector<double>, or a PETSc or Trilinos vector if deal.II is compiled to support these libraries. It is in the responsibility of the caller to assure that the types of the numbers stored in input and output vectors are compatible and with similar accuracy. The ConstraintMatrix passed as an argument to this function makes sure that constraints are correctly distributed when the dof values are calculated.

This function is the counterpart to get_dof_values(): it takes a vector of values for the degrees of freedom of the cell pointed to by this iterator and writes these values into the global data vector values. This function is only callable for active cells.

Note that for continuous finite elements, calling this function affects the dof values on neighboring cells as well. It may also violate continuity requirements for hanging nodes, if neighboring cells are less refined than the present one. These requirements are not taken care of and must be enforced by the user afterwards.

The vector has to have the right size before being passed to this function.

The output vector may be either a Vector<float>, Vector<double>, or a BlockVector<double>, or a PETSc vector if deal.II is compiled to support these libraries. It is in the responsibility of the caller to assure that the types of the numbers stored in input and output vectors are compatible and with similar accuracy.

Return the interpolation of the given finite element function to the present cell. In the simplest case, the cell is a terminal one, i.e., it has no children; then, the returned value is the vector of nodal values on that cell. You could as well get the desired values through the get_dof_values function. In the other case, when the cell has children, we use the restriction matrices provided by the finite element class to compute the interpolation from the children to the present cell.

If the cell is part of a hp::DoFHandler object, cells only have an associated finite element space if they are active. However, this function is supposed to also provide information on inactive cells with children. Consequently, it carries a third argument that can be used in the hp context that denotes the finite element space we are supposed to interpolate onto. If the cell is active, this function then obtains the finite element function from the values vector on this cell and interpolates it onto the space described by the fe_indexth element of the hp::FECollection associated with the hp::DoFHandler of which this cell is a part of. If the cell is not active, then we first perform this interpolation on all of its terminal children and then interpolate this function down to the cell requested keeping the function space the same.

It is assumed that both input vectors already have the right size beforehand.

Note

Unlike the get_dof_values() function, this function is only available on cells, rather than on lines, quads, and hexes, since interpolation is presently only provided for cells by the finite element classes.

This function is the counterpart to get_interpolated_dof_values(): you specify the dof values on a cell and these are interpolated to the children of the present cell and set on the terminal cells.

In principle, it works as follows: if the cell pointed to by this object is terminal (i.e., has no children), then the dof values are set in the global data vector by calling the set_dof_values() function; otherwise, the values are prolonged to each of the children and this function is called for each of them.

Using the get_interpolated_dof_values() and this function, you can compute the interpolation of a finite element function to a coarser grid by first getting the interpolated solution on a cell of the coarse grid and afterwards redistributing it using this function.

Note that for continuous finite elements, calling this function affects the dof values on neighboring cells as well. It may also violate continuity requirements for hanging nodes, if neighboring cells are less refined than the present one, or if their children are less refined than the children of this cell. These requirements are not taken care of and must be enforced by the user afterward.

If the cell is part of a hp::DoFHandler object, cells only have an associated finite element space if they are active. However, this function is supposed to also work on inactive cells with children. Consequently, it carries a third argument that can be used in the hp context that denotes the finite element space we are supposed to interpret the input vector of this function in. If the cell is active, this function then interpolates the input vector interpreted as an element of the space described by the fe_indexth element of the hp::FECollection associated with the hp::DoFHandler of which this cell is a part of, and interpolates it into the space that is associated with this cell. On the other hand, if the cell is not active, then we first perform this interpolation from this cell to its children using the given fe_index until we end up on an active cell, at which point we follow the procedure outlined at the beginning of the paragraph.

It is assumed that both vectors already have the right size beforehand. This function relies on the existence of a natural interpolation property of finite element spaces of a cell to its children, denoted by the prolongation matrices of finite element classes. For some elements, the spaces on coarse and fine grids are not nested, in which case the interpolation to a child is not the identity; refer to the documentation of the respective finite element class for a description of what the prolongation matrices represent in this case.

Note

Unlike the get_dof_values() function, this function is only available on cells, rather than on lines, quads, and hexes, since interpolation is presently only provided for cells by the finite element classes.

Distribute a local (cell based) vector in iterator format to a global one by mapping the local numbering of the degrees of freedom to the global one and entering the local values into the global vector.

The elements are added up to the elements in the global vector, rather than just set, since this is usually what one wants.

Distribute a local (cell based) vector in iterator format to a global one by mapping the local numbering of the degrees of freedom to the global one and entering the local values into the global vector.

The elements are added up to the elements in the global vector, rather than just set, since this is usually what one wants. Moreover, the ConstraintMatrix passed to this function makes sure that also constraints are eliminated in this process.

This function does much the same as the distribute_local_to_global(Vector,Vector) function, but operates on matrices instead of vectors. If the matrix type is a sparse matrix then it is supposed to have non-zero entry slots where required.

Return the global indices of the degrees of freedom located on this object in the standard ordering defined by the finite element (i.e., dofs on vertex 0, dofs on vertex 1, etc, dofs on line 0, dofs on line 1, etc, dofs on quad 0, etc.) This function is only available on active objects (see this glossary entry).

Parameters

[out]

dof_indices

The vector into which the indices will be written. It has to have the right size (namely, fe.dofs_per_cell, fe.dofs_per_face, or fe.dofs_per_line, depending on which kind of object this function is called) before being passed to this function.

This function reimplements the same function in the base class. In contrast to the function in the base class, we do not need the fe_index here because there is always a unique finite element index on cells.

In many places in the tutorial and elsewhere in the library, the argument to this function is called local_dof_indices by convention. The name is not meant to indicate the local numbers of degrees of freedom (which are always between zero and fe.dofs_per_cell) but instead that the returned values are the global indices of those degrees of freedom that are located locally on the current cell.

Return the finite element that is used on the cell pointed to by this iterator. For non-hp DoF handlers, this is of course always the same element, independent of the cell we are presently on, but for hp DoF handlers, this may change from cell to cell.

Note

Since degrees of freedoms only exist on active cells for hp::DoFHandler (i.e., there is currently no implementation of multilevel hp::DoFHandler objects), it does not make sense to query the finite element on non-active cells since they do not have finite element spaces associated with them without having any degrees of freedom. Consequently, this function will produce an exception when called on non-active cells.

Since degrees of freedoms only exist on active cells for hp::DoFHandler (i.e., there is currently no implementation of multilevel hp::DoFHandler objects), it does not make sense to query active FE indices on non-active cells since they do not have finite element spaces associated with them without having any degrees of freedom. Consequently, this function will produce an exception when called on non-active cells.

Set the index of the FiniteElement used for this cell. This determines which element in an hp::FECollection to use. This function is only useful if the DoF handler object associated with the current cell is an hp::DoFHandler.

Note

Since degrees of freedoms only exist on active cells for hp::DoFHandler (i.e., there is currently no implementation of multilevel hp::DoFHandler objects), it does not make sense to assign active FE indices to non-active cells since they do not have finite element spaces associated with them without having any degrees of freedom. Consequently, this function will produce an exception when called on non-active cells.

When using parallel meshes, either through the parallel::shared::Triangulation or parallel::distributed::Triangulation classes, it is only allowed to call this function on locally owned cells (see this glossary entry). This is because otherwise a common source of errors would be if one processor sets a different active_fe_index on a ghost cell than the processor that actually owns the cell does. To avoid this mistake, one can only set active_fe_index information on locally owned cells, and this information is then mirrored to all processors that have this cell as a ghost cell – see the documentation of the hp::DoFHandler class.